1. Field of the Invention
The present invention relates to hydraulically actuated fuel injectors of the type having a pressure intensifier, and to the use of rate shaping in fuel injectors for obtaining reduced emissions.
2. Description of Related Art
The use of injection rate shaping (i.e., changing of the injection rate during the injection of fuel by a fuel injector into an engine) for reducing NO.sub.x emissions is known. For example, in U.S. Pat. Nos. 4,718,384, 4,627,571, and 3,669,360, injection rate shaping, producing a lower initial rate of injection and a higher subsequent rate of injection, is achieved by varying the pressure acting on a needle valve at the outlet end of the injector so as to initially restrict the extent that the needle valve opens and then allowing it to open to a greater extent for increased fuel flow. However, these arrangements are not in hydraulically actuated fuel injectors having pressure intensifiers and they are limited to use with closed nozzle fuel injectors, i.e., those having a needle valve at the outlet end thereof. Furthermore, if highly pressurized fuel (for example, 15-20 kpsi) is delivered to these injectors, obtaining of a precise flow rate control will be difficult to achieve.
Likewise, known techniques for producing a two stage (preliminary and main injection) process (e.g., U.S. Pat. Nos. 4,601,269 and 3,404,861) as well as for producing an initially restricted flow of fuel followed by an unrestricted flow of fuel to the injector (e.g., U.S. Pat. No. 3,747,857) also possess deficiencies with respect to the supplying of precisely metered quantities of fuel at very high pressures in a way applicable to a variety of different types of injectors.